(1) Field of the Invention
This invention relates to an electrodialysis anion selective membrane which may be used for effectively recovering and concentrating an acid from dilute acid solutions, mixtures of acids and salts or mixtures of acids and water-soluble organic compounds by electrodialysis, and to methods of producing such membranes. More particularly, this invention relates to an anion electrodialysis membrane having a high current efficiency and low electrical resistance in acid solutions.
(2) Description of the Prior Art
The anion selective membrane of this invention retards the passage of hydrogen (H.sup.+) ions but readily allows the flow of anions such as chloride, (Cl.sup.-) ions when in contact with an acid-containing solution, and while under an applied D.C. potential. With such a membrane, one can efficiently concentrate or deacidify acidic solutions by the electrodialysis process.
Commercially available anion selective membranes such as for example the aliphatic quaternary ammonium anion exchange membrane described in U.S. Pat. No. 4,231,855 (Hodgdon, et. al.) permit substantial passage of hydrogen ions when used for the electrodialysis of acid solutions, resulting in poor anion transfer current efficiency and high equipment and energy costs. Such drawbacks have precluded the extensive application of electrodialysis to the processing of acid-containing solutions.
Uses for the novel membrane of the present invention are in the recovery of acid-containing solutions which become `spent` when their salt concentration becomes too high, or where the acid concentration is too low. These types of acid/salt solutions are encountered in such operations as the metal finishing, plating and mining industries. At present, these acid/salt solutions have become a waste disposal problem for their respective industries since there are few efficient remedies to the problem of removing acids from `spent` solutions and recovering said acid at useful concentrations.